Dunkleosteus
Dunkleosteus is a genus of prehistoric fish, one of the largest arthrodire placoderms ever to have lived, existing during the Late Devonian period, about 380-360 million years ago. This hunter, measuring up to 10 metres and weighing 3.6 tons was a hypercarnivorous apex predator. Few other placoderms, save, perhaps, its contemporary, Titanichthys, rivaled Dunkleosteus in size. Dunkleosteus is a member of the pachyosteomorph athrodires, and is more specifically usually placed in the family composed mostly of large, carnivorous athrodires like Gorgonichthys. Anderson suggets that because of its primitive jaw structure Dunkleosteus should be placed outside the family Dinichthyidae, perhaps close to the base of the clade Pachyosteomorpha, near Eastmanosteus, but this idea has yet to be tested. New studies have revealed several features in both its food and biomechanics as its ecology and physiology. Placodermi first appeared in the Silurian, and the group became extinct during the transition from the Devonian to the Carboniferous, leaving no descendants. The class lasted barely 50 million years, in comparison to the 400 million year long history of sharks. In recent decades, Dunkleosteus has achieved recongnition in popular culture, with a large of specimens on display, and notable appearances in entertainment media. Numerous fossils of some species have been found in North America, Poland, Belgium and Morocco. Description Due to its heavily armoured nature, Dunkleosteus was likely a relatively slow, but powerful,swimmer . It is thought to have dwelled in diverse zones of inshore waters. Fossilization tends to have preserved only the especially armoured frontal sections of his ancient fish like. As such, the reconstructions of the hindquarters are often based on smaller arthrodires, such as Coccosteus,that had hind sections preserved. The most famous specimens of Dunkleosteus are display at the Cleveland Museum of Natural History. Others are displayed at the American Museum of Natural Museum of Natural History and in the Queensland Museum in Brisbane, Queensland. Instead of teeth , Dunkleosteus possessed two pairs of sharp bony plates which formed a beak-like structure. After studying a biomechanical model of the fish's jaws, scientists at the Field Museum of Natural History and the University of Chicago concluded that Dunkleosteus had the second most powerful bite of any fish. Dunkleosteus could create a pressure of 1,100 pounds per square inch and up to 1,800 pounds per square inch at tip of its fangs, placing Dunkleosteus in the same league as Tyrannosaurus and morden crocodiles as having the most powerful known bite . Dunkleosteus could open it's mouth in one-fiftieth of a second, which would have caused a powerful suction that pulled the prey into it's mouth, a food capture technique used by many fish today. '' '' The discovery of Dunkleosteus armor with unhealed bite marks strongly suggest that they cannibalized each other when the opportunity arose. Frequently, fossils of Dunkleosteus are found with boluses of fish bone, semi-digested and partially eaten remains of other fish. As a result, the fossil record indicates that it may have routinely regurgitaded prey bones rather than digest them. Dunkleosteus, together with most other placoderms, may have also been among the first vertebrates to internalize egg fertilization, as seen in some modern sharks. Morphological studies done on "jaws bones" of juvenile and adult Dunkleosteus suggest that Dunkleosteus went through a change in jaw morphology and diet as it age. Juvenils had stiffer jaws more similar to Coccoteus, and appeard to have on varies soft-bodied aquatic animals. The jaws of adults were more flexible to hold struggling prey, and were well equipped to bite through the bony armor of hard-bodied animals like other placoderms. Species There have been at least ten different species of Dunkleosteus described so far. D.terrelli This is the largest, best known species of genus. It has a rounded snout. D.terrelli fossil remains are found in Upper Fammennian to Upper Fransnian Late Devonian strata of the United States and Europe. D.belgicus Known from fragments described from the Fammenian of Belgium. The median dorsal plate is characteristic of the genus, but, a plate that was described as a suborbital is apparently an anterior-laterol plate. D.denisoni Known from a small median dorsal plate'','' typical in'' appearance for Dunkleosteus,'' 'but'' much small than ''normal. D.marsaisi D.marsaisi was refers to the Dunkleosteus fossils from the Lower Fammenian Late Devonian strata of the Altas Mountains in Morocco. It differs in size, the known skulls averaging a length of 35 centimetres and in form to D.terrelli. In D.marsaisi, the snout is more narrow, and there may be a postpineal fenestra present. Many researchers and authorities consider it a synonym of D.terrelli. H.Schultze regards D.marsaisi as a member of Eastmanosteus. D.mangnificus A large placoderm from the Frasnian Rhinestreet shale of New York. It was originally described as Dinichthys mangnificus by Hussakof and Bryant in 1919, then as Dinichthys mirabilis by Heintz in 1932. Dunkle and Lane moved it to Dunkleosteus in 1971. D.missouriensis Known from fragments from Frasnian Missouri. Dunkle and Lane regard them as being very similar to D.terrelli. D.newberryi Known primarily from a 28 centimetre long infragnathal that has a prominent anterior cusp. Found in the Frasnian portion of the Genesee group of New York, and originally described as Dinichthys newberryi. D.amblyodoratus D.amblyodoratus is known from some frangmentary remains from Late Devonian strata of Kettle Point, Canada. The species name means blunt spear, and refers to the way the nuchal and paranuchal plates in the back of the head form the shape of a blunted spearhead. Although it is known only from fragments, it is estimated to have been about 20 feet long in life. D.raveri D.raveri is a small, possibly 1-metre-long species known from an uncrushed skull roof, found in a carbonate concretion from near the bottom of the Huron Shale, of the Famenian Ohio Scale strata. Besides its small size, it had comparatively large eyes. Because D.raveri was found in the strata directly below the remains of D.terrelli. The species name commemorates Clarence Raver of Wakeman, Ohio, U.S, who discovered the concretion the holotype was found in. History Dunkleosteus was named in 1956 to honour David Dunkle, then curator of Veterbrate Paleontology at the Cleveland Museum of Natural History. The type species was originally described in 1873 as a species of Dinichthys.